The pharmaceutically acceptable acid addition salts of Labetalol and its isomers and mixtures thereof are useful cardiovascular drugs used, for instance, in the treatment of hypertension and cardiac arrhythmias. See, for instance, U.S. Pat. No. 4,012,444, British Pat. Nos. 1,541,932 and 1,541,933, and U.S. Ser. No. 089,077, filed Oct. 29, 1979, of common assignee as the instant application. Labetalol hydrochloride is marketed, e.g., in Great Britain, in an injectable formulation under the trade name Trandate.RTM.. The formulation marketed consists of 5.0 mg/ml labetalol hydrochloride, 8.1 mg/ml sodium chloride and sterile water for injection. This formulation has been found to be unsuitable for long-term shelf life due to the formation of particulate matter when stored for 3 months at temperatures of 45.degree.-55.degree. C. or at refrigerator temperature (5.degree.-6.degree. C.)